In order to become a Christian believer do I have to undertake any hard study?
Not at all! Understanding with one’s mind and believing, are two entirely different issues. Regardless of how much they study some people simply cannot believe, while there are others who can intuitively understand their faith with their hearts, even if they don’t study much. However, if you really wish to deepen your faith and enable it to grow, I would recommend you engage in proper study, as far as your circumstances permit. Human beings are not composed merely of the head or merely of the heart. Like the two wheels of a car, we need to maintain a balance between faith and reason. Faith is something that also requires some understanding, in order that we may not get overwhelmed with passion or run in the wrong direction.
How much study would a particular individual need? I guess that would vary from person to person. It would depend on the individual’s interests, personality, age, health, time, and other factors. If you were to participate in an introductory course offered by a Church or other such institution, it would depend upon the judgment of the priest or other responsible persons who instruct you, to decide whether you are fully prepared to become a believer or not.